BRITISH AVONIAN CONODONT FAUNAS 81 
DEscRIPTION. The margin of the outer parapet of the platform is straight and 
that of the inner parapet, convex. A deep trough is developed for the greater part 
of the length of the platform, except for the posterior quarter of the platform, where 
there is a short carina, which bears a few nodes. The platform is ornamented by a 
number of transverse ridges of medium length, which extend into the trough. In 
oral view the flaring of the basal cavity on its inner side is seen. 
The anterior blade, which rises out of the outer parapet, slopes slightly towards the 
anterior. The posterior three denticles of the anterior blade are highest. The 
anterior edge of the anterior blade and the posterior edge of the platform are of equal 
elevation. Half the length of the anterior blade is free. Aborally, the basal cavity is 
asymmetrical and flared, there being a greater flare on the inner side than on the 
outer. 
REMARKS. This species closely resembles Cavusgnathus convexus but differs from 
the latter in that the basal cavity does not extend to the posterior extremity of the 
unit. In addition C. convexus rarely bears a carina and has fewer and shorter ridges 
in the surface ornamentation. 
The present specimens show an even closer similarity to C. regularis Youngquist & 
Miller (as interpreted by Rexroad & Nicoll 1965, Pl. 1, figs. 16, 17) and this species 
may be a junior synonym of C. cristatus Branson & Mehl. 
Cavusgnathus naviculus (Hinde) 
Plate 13, figs. 1za-d. Plate 14, figs. 1a—d, 4a—6d 
1900 Polygnathus navicula Hinde : 342, Pl. 9, fig. 5. 
1928 Polygnathus navicula Hinde ; Holmes: 18, Pl. 7, fig. 14. 
1947 Cavusgnathus cristata Branson & Mehl ; Cooper (partim) : 91, Pl. 20, figs. 7-10. 
1957 Cavusgnathus cristata Branson & Mehl ; Bischoff: 19, Pl. 2, figs. 7a, b. 
1960 Cavusgnathus navicula (Hinde) Clarke : 23, Pl. 4, figs. 1-3. 
1960 Cavusgnathus inflexa Clarke : 23, Pl. 3, figs. 17, 19. 
1961 Cavusgnathus navicula (Hinde) Rexroad & Burton: 1151, Pl. 1309, figs. 4-13. 
1965 Cavusgnathus navicula (Hinde) Rexroad & Nicoll: 17, 18, Pl. 1, figs. 24, 25. 
MATERIAL. 9 Specimens: figured, X 65, X 66, X 67, X 68, X 69. 
Rance. North Crop 3D 22, Avon Gorge D 26. 
DESCRIPTION. Unit slender and elongate in lateral view with short blade ; 
long, tapering inner and outer lateral sides which are almost straight in oral view, 
and are about two to three times as long as the blade. In oral view they are abruptly 
tapered in their posterior quarter, and the lateral edges are finely serrated. The oral 
surface is decorated by transverse lateral ridges, which converge, but do not meet, 
towards the narrow, shallow central trough. This trough is deepest in the anterior 
third ; on the inner lateral oral surface the ridges are obsolescent and are replaced 
by rounded nodes. There are about Io transverse ridges on the outer lateral face. 
In the posterior third of the unit there is the development of a rather inconspicuous 
carina, consisting of fine, elongate, node-like denticles joined by a thin median ridge. 
The inner lateral aboral flange is conspicuous in oral view. 
